This invention relates generally to motors and specifically to an electromagnetic motor having an insert for controlling end play of an armature therein.
Direct current (dc) electromagnetic motors are used in automotive vehicles for various purposes. For example, dc motors are used in automobiles to operate window lifts, windshield wipers, anti-lock braking systems, seat adjustments, and other devices. The motors often have a housing with a longitudinally extending bore within which is journalled an armature and an armature shaft positioned in operative association with a fixed stator. Maintaining a proper longitudinal internal clearance or end play of the armature shaft relative to the associated stator and housing is important in the operation of the motor. Insufficient clearance between the longitudinal ends of the armature shaft and adjacent portion of the housing results in excessive wear and may prevent fractional horsepower motors from starting. On the other hand, excessive clearance results in objectional end bumping noises when the armature shaft thrusts back and forth during start up or directional changes of the motor. Excessive clearance can further create alignment problems between the armature shaft and associated driven components such as gears, cables and the like.
The end of the armature shaft is conventionally supported by means of a threaded bolt and a locking nut which are inserted into a tunnel concentrically intersecting the housing bore proximate with a distal end of the armature shaft. This conventional method, however, often requires extra water seals, is relatively time consuming and costly to assemble, and is operator sensitive. Another conventional end support device consists of injection molding a plastic plug into the tunnel of the housing. This plastic plug is allowed to cool, thereby shrinking, thus creating a clearance to the armature shaft. Also, a variety of inserted shims are used between the end of the armature shaft and an adjacent abutting end of the housing. While these traditional devices have improved the end play control of the armature shaft relative to the adjacent housing, the aforementioned motors are costly to manufacture and still have end play clearance problems.
Other devices and methods for reducing end play are disclosed in the following U.S. Pat. Nos. 5,144,738 entitled "Automatic Retention Adjustment of Motor Armature Assembly," which issued to Oyafuso on Sep. 8, 1992; 4,914,332 entitled "Dynamoelectric Machine Shaft Restrictor for Controlling End Play," which issued to Borcherding et al. on Apr. 3, 1990; 4,455,498 entitled "Means for Adjusting Motor End Play," which issued to DeSisto on Jun. 19, 1984, all of which are incorporated by reference herewithin. Alternately, U.S. Pat. No. 4,199,861 entitled "Method of Making An End Play Control Assembly," which issued to Buckman et al. on Apr. 29, 1980 teaches using an ultrasonic weld to join a bushing and a thrust collar together around one end of the motor shaft so as to rotate with the shaft; this is also incorporated by reference herewithin.
Accordingly, it would be desirable to have a motor with an automatically adjustable end play insert set to account for each motor's specific tolerance conditions.